MacMurrough (Mac Murchadha), Art (d. 1362), king of Leinster, was eldest son of Muircheartach mac Muiris MacMurrough, king of Leinster. He may be the man captured with Henry Trahene, seneschal of Carlow, by the Butlers in 1326. Very little else is known of his early career except that he married his first cousin, the daughter of Pilib O'Byrne. With O'Byrne aid, Muircheartach and his brothers assumed the leadership of their dynasty after the assassination of their cousin Domhnall MacMurrough (qv) on 5 July 1347. They were on good terms with the English, as evidenced by their hostility to John O'Byrne (Seán Ó Broin) in 1353. After his submission (April 1354) they realigned themselves with him and attacked the English. The elder MacMurrough was quickly captured but Art and O'Byrne defeated Justicar Thomas Rokeby (qv), besieging him in Wicklow castle (October 1354). Muircheartach was brought by sea to Wicklow and executed as a warning to his son.
During 1355 Art remained at war, but he submitted before the end of the year. Between 1355 and 1357 he reconciled himself with Domhnall's sons and the English by fighting the Leinster Irish (February–April 1357). For his efforts, he was recognised as head of his lineage by Edward III and granted a fee. By May 1358 he (with the O'Mores) was openly defying the English by threatening their settlements along the Barrow. Later in 1358 he met with English officials at Athy, but proved belligerent. By shrewd diplomacy he welded the Leinster Irish into a confederation and brought incessant pressure to bear on the English settlers of the Barrow and the Leinster mountains. In 1359, amid an offensive by Art in Laois, James Butler (qv), 2nd earl of Ormond, voiced his belief that the Irish assaults were coordinated. Art's plans were foiled when Ormond defeated him in August 1359, but continuing Irish pressure in Leinster brought Lionel of Clarence (qv) to Ireland in September 1361. Despite an initial reverse in Wicklow, Clarence decided to shore up the English position along the Barrow by refortifying Carlow and removing Art. According to Froissart's chronicle, Lionel achieved a pyrrhic victory over the Leinster king. Later at parley before the end of the year, Clarence treacherously captured Art and his tánaiste. They were confined in Trim castle, where Art was either killed or died in July 1362. His brother Donnchadh Caomhánach MacMurrough (c.1315–75) and successor Diarmaid Láimhdhearg MacMurrough received fees from Clarence during 1364. But their threat to the Barrow conduit remained, as evinced by the executions of Art's brother Gearóid and Diarmait Láimhdhearg (1369). Donnchadh Caomhánach continued this expansion till Geoffrey de Valle, sheriff of Carlow, killed him on 26 July 1375.